This invention relates to an etching solution, an etching method and a method for manufacturing a semiconductor device. More particularly, the invention relates to an etching solution adapted for use in etching at the time of forming copper wiring, an etching method using the etching solution, and a method for manufacturing a semiconductor device using the etching method.
Copper wirings having a conventional groove wiring structure are formed in the following way. More particularly, as shown in FIG. 11A, copper 116 made of a copper seed layer 114 and a copper plated layer 115 is buried in a wiring groove 112 formed in an insulating film 111 via a barrier layer 113. Thereafter, additional copper 116 on the insulating film 111 is removed by chemical mechanical polishing (hereinafter referred to simply as CMP). In addition, an additional barrier layer 113 over the insulating film 111 is also removed by CMP making use of a polishing slurry for a barrier layer which is different from one used in the CMP for copper. As a consequence, a groove wiring 117 is formed of the copper 116 left within the wiring groove 112 through the barrier layer 113 as shown in FIG. 11B.
In this arrangement, however, as miniaturization of the wiring groove 112 proceeds, a difficulty is involved in forming, in good coverage, the barrier layer formed by a sputtering technique and made of tantalum, tantalum nitride or the like. To cope with this, attempts have been made to use, as a barrier layer, tungsten, tungsten nitride, titanium or titanium nitride that can be formed as a film according to a chemical vapor deposition technique (hereinafter referred to simply as CVD) ensuring good coverage. With the barrier layer 113 formed of a tungsten material such as tungsten, tungsten nitride or the like, or titanium that is likely to undergo film formation by CVD, so-called galvanic corrosion is caused wherein such a barrier layer 113 is corroded in the CMP step of removing additional copper (not shown) over the insulating film 111 (see, for example, “New materials/process technologies for Multi-layered Wirings for Next General ULSI”, published by Kazuhiro Takausu (publisher) of Technical Information Institute Co., Ltd., and issued on Dec. 27, 2000 (first edition), pp. 249 to 252).
The galvanic corrosion occurs in such a way that when materials, such as tungsten, tungsten nitride, titanium and the like, whose potential relative to copper differs greatly (e.g. with a difference of about 1 V or over) and which have a potential poorer than copper is used, these materials are dissolved out in the polishing solution. Disappeared portions (fine interstices) 121 at the barrier layer 113, which result from the galvanic corrosion, can be suppressed to a degree of recess (or gap) of 10 nm or below by adjusting the pH of a slurry, forming a current barrier layer through oxidation of the copper, and minimizing the amount of an oxidizing agent for copper.